Ideally, a speaker enclosure should be provide with an infinite baffle. It is therefore very important for a speaker enclosure to provide therein means for adequately treating the sound pressure directed towards the reat of the speaker enclosure.
Up to date, various attempts were made about speaker enclosures so as to properly treat the sound pressure, as disclosed, for instance, in U.S. Pat. Nos. 4,167,985, 4,421,200 and 4,433,749. Examples of such known speaker enclosures are closed baffle type enclosures (FIG. 27), bass reflex type enclosures (FIG. 28), drown cone type enclosures (FIG. 29) and back load horn type enclosures (FIG. 30).
As shown in these figures, speaker enclosures 2 of base reflex type, drown cone type and back load horn type are provided with an opening 3 or a drown cone 4 in order to adequately use the sound pressure directed towards the rear of speaker 1a. The opening 3 serves as an exit for the bass sound with a phase-inverted portion. Speaker enclosures of these three types can produce clear sounds with a high efficiency at lower frequency portions thereof. However, in these speaker enclosures, the air suspension which controls the speaker vibration system, is rather weak. Furthermore, there is a resonance frequency determined by the duct length and by the drown cone, so that there is such a tendency that a somewhat colored or plain sound is generated.
Closed baffle type speaker enclosures include acoustic suspension type enclosures and air suspension type enclosures. The acoustic suspension type speaker enclosures are so designed that a large amount of sound absorptive materials is placed in the enclosures so as to absorb that portion of the sounds radiated from each speaker that is directed towards the rear of the speaker enclosure systems, thereby serving in eliminating any leakage of that portion of sounds from the enclosures. In a speaker enclosure of the air suspension type, use is made of a speaker 1 with a low value of the minimum resonance frequency (fo) in such a mammer that the vibration system of the speaker 1 is supported on an air suspension kept in the closed enclosure (2). These closed baffle type speaker enclosures 2 do not generate unclear bass sounds, but the enclosures have the following shortcomings: there is a resistance to the vibration of a cone paper 1b so that a stuffy and unclear sound is radiated: there is a resonance causing an excessive rebound of the air suspension; and there is a standing wave so that a distorted sound is produced.